Optical Coherence Tomography (OCT) is a technique for performing high-resolution cross-sectional imaging that can provide images of tissue structure on the micron scale in situ and in real time (Huang et al. “Optical Coherence Tomography” Science 254(5035):1178 1991). OCT is a method of interferometry that determines the scattering profile of a sample along the OCT beam. Each scattering profile is called an axial scan, or A-scan. Cross-sectional images (B-scans), and by extension 3D volumes, are built up from many A-scans, with the OCT beam moved to a set of transverse locations on the sample. OCT provides a mechanism for micrometer resolution measurements.
In frequency domain OCT (FD-OCT), the interferometric signal between light from a reference and the back-scattered light from a sample point is recorded in the frequency domain rather than the time domain. After a wavelength calibration, a one-dimensional Fourier transform is taken to obtain an A-line spatial distribution of the object scattering potential. The spectral information discrimination in FD-OCT is typically accomplished by using a dispersive spectrometer in the detection arm in the case of spectral-domain OCT (SD-OCT) or rapidly scanning a swept laser source in the case of swept-source OCT (SS-OCT).
Evaluation of biological materials using OCT was first disclosed in the early 1990's (see for example U.S. Pat. No. 5,321,501). Frequency domain OCT techniques have been applied to living samples (see for example Nassif et al. “In vivo human retinal imaging by ultrahigh-speed spectral domain optical coherence tomography” Optics Letters 29(5):480 2004). The frequency domain techniques have significant advantages in speed and signal-to-noise ratio as compared to time domain OCT (see for example Choma, M. A., et al. “Sensitivity advantage of swept source and Fourier domain optical coherence tomography” Optics Express 11(18): 2183 2003). The greater speed of modern OCT systems allows the acquisition of larger data sets, including 3D volume images of human tissue. OCT has found widespread use in the field of ophthalmology as evidenced by numerous commercially available ophthalmic OCT devices including the Stratus, Cirrus HD-OCT, and Visante (Carl Zeiss Meditec, Inc. Dublin, Calif.). Technology development in the field continues with efforts towards increasing the ease of use of the instruments, improving analytic functionality and increasing reliability of data when imaging patients with various abnormalities.